2: static char help[] = "Tests repeated use of assembly for matrices.\n\
  3:  does nasty case where matrix must be rebuilt.\n\n";

  5:  #include <petscmat.h>

  7: int main(int argc,char **args)
  8: {
  9:   Mat            C;
 10:   PetscInt       i,j,m = 5,n = 2,Ii,J;
 12:   PetscMPIInt    rank,size;
 13:   PetscScalar    v;
 14:   Vec            x,y;

 16:   PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
 17:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
 18:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
 19:   n    = 2*size;

 21:   /* Create the matrix for the five point stencil, YET AGAIN */
 22:   MatCreate(PETSC_COMM_WORLD,&C);
 23:   MatSetSizes(C,PETSC_DECIDE,PETSC_DECIDE,m*n,m*n);
 24:   MatSetFromOptions(C);
 25:   for (i=0; i<m; i++) {
 26:     for (j=2*rank; j<2*rank+2; j++) {
 27:       v = -1.0;  Ii = j + n*i;
 28:       if (i>0)   {J = Ii - n; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
 29:       if (i<m-1) {J = Ii + n; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
 30:       if (j>0)   {J = Ii - 1; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
 31:       if (j<n-1) {J = Ii + 1; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
 32:       v = 4.0; MatSetValues(C,1,&Ii,1,&Ii,&v,INSERT_VALUES);
 33:     }
 34:   }
 35:   MatAssemblyBegin(C,MAT_FINAL_ASSEMBLY);
 36:   MatAssemblyEnd(C,MAT_FINAL_ASSEMBLY);
 37:   for (i=0; i<m; i++) {
 38:     for (j=2*rank; j<2*rank+2; j++) {
 39:       v = 1.0;  Ii = j + n*i;
 40:       if (i>0)   {J = Ii - n; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
 41:       if (i<m-1) {J = Ii + n; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
 42:       if (j>0)   {J = Ii - 1; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
 43:       if (j<n-1) {J = Ii + 1; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
 44:       v = -4.0; MatSetValues(C,1,&Ii,1,&Ii,&v,INSERT_VALUES);
 45:     }
 46:   }
 47:   /* Introduce new nonzero that requires new construction for
 48:       matrix-vector product */
 49:   if (rank) {
 50:     Ii   = rank-1; J = m*n-1;
 51:     MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);
 52:   }
 53:   MatAssemblyBegin(C,MAT_FINAL_ASSEMBLY);
 54:   MatAssemblyEnd(C,MAT_FINAL_ASSEMBLY);

 56:   MatView(C,PETSC_VIEWER_STDOUT_WORLD);

 58:   /* Form a couple of vectors to test matrix-vector product */
 59:   VecCreate(PETSC_COMM_WORLD,&x);
 60:   VecSetSizes(x,PETSC_DECIDE,m*n);
 61:   VecSetFromOptions(x);
 62:   VecDuplicate(x,&y);
 63:   v    = 1.0; VecSet(x,v);
 64:   MatMult(C,x,y);

 66:   MatDestroy(&C);
 67:   VecDestroy(&x);
 68:   VecDestroy(&y);
 69:   PetscFinalize();
 70:   return ierr;
 71: }